Oxidized and polymer-modified bitumens are frequently used as a backing material in the manufacture of carpet tiles. The construction of these tiles are fairly complex and may consist of a fibrous, e.g. tufted, primary cloth which has been impregnated with a cured latex to stabilize the tufting, and laminated to a secondary backing cloth using the aforementioned bitumen.
In this application, severe physical demands are placed on the bitumen to control stress relaxation in the primary tufting cloth, to maintain and retain critical physical dimensions over a wide range of possible application conditions, to prevent excessive build up to static electricity which may damage electrical and computer hardware as well as physical discomfort to building occupants; and to maintain physical dimensions under static loading conditions such as would occur when heavy objects are placed on carpet tiles over an extended period of time.
The bitumen used must also possess characteristics in the molten phase which will allow easy preparation and processing, i.e. a suitable viscosity at application temperatures with maximum thermal stability and minimum dimensional instability when applied to the manufactured product.
It has been proposed in U.K. patent application GB 2 219 802 A (Vulcanite Ltd.) to incorporate a low density polyethylene into bitumen for roofing and carpet tile backing purposes. It has been found that such blends do not fulfill all of the demands placed on a bitumen used in the contact of a carpet tile backing. The static loading and dimensional stability of a carpet tile produced using such a bitumen would not be commercially acceptable and would fall outside the standard requirements laid down by the carpet tile and floor laminating industry.
Self-adhesive bitumen compositions containing polyethylene or crystalline polypropylene have been suggested for use in carpet tiles with a self-adhesive backing in GB Pat. 1 417 571 (Ruberoid Ltd.). Further, carpet tiles have been prepared employing a blend of bitumen and a minor amount of a thermoplastic styrene-butadiene-styrene block copolymer (SBS) as the integral backing layer styrene-butadiene-styrene block copolymer (SBS) as the integral backing layer in U.S. Pat. 4,201,812 (Shell Oil Company). However, the block copolymer presents processing, compatibility, cost and other difficulties in its use as a carpet backing blend.